An extruder die for the extrusion of a multilayer thermoplastic laminate, particularly in the form of a foil or plate, comprises a multicomponent block symmetric with respect to a central symmetric plane with respect to the feed channels and distributing channels connected to the feed channels, at least one mouth and central distributor channel connected to the mouth symmetric in relation to the axis of the extruder die as well as an outlet die following the central distributor channel.
The block on the end opposite the outlet die has an additional feed channel with a round or rectangular cross section for feeding in a special plastic material. The additional feed channel becomes a discharge duct extending to the mouth downstream.
The term "special plastic material" is used for the central layer and this layer is generally used to form a barrier layer which is impervious to moisture or gases. A typical plastic material is for example PVdC. The special plastic material is frequently temperature sensitive. On the other hand for the purpose of a satisfactory bonding with the usual plastic material the special plastic material must have a temperature which coincides sufficiently with the standard plastic material.
In a known extruder die (Plastics World, August 1984, p.17) a passage in the block forms an additional feed channel. A nickel sleeve is inserted in this passage. An automatic tempering (temperature control) of the special plastic flow in the additional feed channel does not occur. The nickel sleeve is scarcely effective as a heat insulator. Accordingly the heat which reaches the thermoplastic material is so great that the block in the vicinity of the additional feed duct is so hot that the special plastic material is damaged on rheological grounds by overheating.